Method and manufacturing of sealed monolithic eletrochemical systems and a sealed monolithic eletrochemical system

ABSTRACT

Method for manufacturing sealed monolithic electrochemical systems, which method comprises the following method steps:  
     application of electrolyte to a pattern of a porous structure located on a substrate, which structure constitutes a monolithic electrochemical electrode and comprises a working electrode, an insulating layer and a counterelectrode  
     application of a sealing material surrounding said porous structure to form a laminate comprising a front plane consisting of said substrate and the porous structure and a rear plane consisting of the sealing material.

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturingsealed monolithic electrochemical systems according to the preamble ofpatent claims 1 and 18, and in particular a method for manufacturingmonolithic electrochemical systems comprising a substrate, a pattern,located on this substrate, of a porous structure comprising a workingelectrode, an insulating layer and a counterelectrode, in which theporous structure is filled with electrolyte before the pattern of theporous structure is encapsulated between the substrate and a rear planeconsisting of a sealing material.

[0002] The present invention also relates to a sealed monolithicelectrochemical system according to the preamble of patent claim 16.

BACKGROUND ART

[0003] From WO97/16838, a method for manufacturing monolithicphotoelectrochemical cells is previously known. In this method,photoelectrochemical cells are formed by virtue of patterns ofconductive material being applied to an electrically insulatedtransparent material. A porous structure is then applied by successiveapplication of a ply of a porous semiconductor, a ply of a porousinsulator and a ply of a porous conductor. After application of theporous structure, the porous structure is provided with a liquidelectrolyte. The porous structure is also covered by an insulating coverlayer.

[0004] It has been found, however, that a number of problems arise inthe sealing of monolithic electrochemical systems. On the one hand, ithas been found that the cells are sensitive to moisture and impuritiesbecause the presence of moisture and impurities has a considerableeffect on the long-term stability of the system. On the other hand, itis important that the sealing along the outer edge of the cellseffectively prevents leakage or dissipation of, on the one hand,electrolyte from inside the cells and, on the other hand, impurities andmoisture from the outside into the cells.

[0005] In order to seal monolithic electrochemical systems, in whichelectrolyte is in place on sealing, various methods have been tried,such as gluing and joining together by pressing between two rollers.None of the methods tried previously has resulted in electrochemicalsystems with sufficiently good long-term characteristics and with asufficiently low degree of impairment of the performance of the cell inthe sealing process, which has also resulted in cost-effectiveindustrial manufacture of electrochemical systems being made moredifficult.

BRIEF DESCRIPTION OF THE INVENTION

[0006] The object of the invention is to provide a method formanufacturing sealed monolithic electrochemical systems, in which therisk of the presence of moisture and impurities in the cell aftersealing is reduced, the long-term stability of the cells is increasedand the sealing has a high degree of impermeability in relation to theenvironment.

[0007] These objects are achieved by a method according to thecharacterizing part of patent claim 1. The sealing material comprises aplastic which is melted and joined together with a front plane,consisting of a substrate and cells located on the substrate. By virtueof the fact that the sealing material is heated and pressed together,sealing is obtained along the edge of the pattern of the porousstructure. The edge means on the one hand the inner edge which separatesthe individual cells in a group of cells from one another and, on theother hand, the outer edge which separates a group of cells from theenvironment. As the plastic layer is very flexible in its heated state,very tight and good sealing is obtained, the risk of moisture andimpurities penetrating being reduced and the long-term stability of thesystem thus being increased. The sealing method according to theinvention also reduces the risk of the performance of the cells beingreduced during the manufacturing process.

[0008] In a preferred embodiment of the invention, the monolithicelectrochemical system is subjected to an underpressure, evacuation ofmoisture and gases from the porous structure being permitted. Thisresults in the possibility of obtaining a cleaner and thus morelong-term stable product.

[0009] In a preferred embodiment of the invention, the front plane andthe rear plane are pressed together by a flexible pressing tool. Bypressing the front plane and the rear plane together with a flexiblepressing tool, good sealing is provided along the edge of the appliedpattern of cells. The good sealing is provided along both an inner edgebetween the individual cells and an outer edge surrounding the cells.The sealing between the cells, that is to say the inner edge, results inthe risk of leakage between the cells being reduced, and the sealingsurrounding the pattern of cells, that is to say the outer edge, reducesthe risk of dirt and moisture penetrating the cells from theenvironment.

[0010] Another object of the invention is to provide a sealed monolithicelectrochemical system comprising an effective protective barrieragainst the penetration of moisture and impurities from the environmentto the cells, in which the risk of degrading of the function of the cellduring encapsulation is reduced, and it is possible for the cells tohave sufficiently good long-term characteristics. These objects areachieved by a sealed monolithic electrochemical system according to thecharacterizing part of patent claim 16. By using a sealing materialwhich comprises at least a first ply which consists of a plastic film, ajoint is provided between the front plane and the rear plane of theelectrochemical system, which reduces the risk of moisture penetratingthe cells and also reduces the risk of electrolyte flowing out from acell and making contact with an adjacent cell. As the plastic layer isvery flexible in its heated state, very tight and good sealing isobtained, the risk of moisture penetrating being reduced and thelong-term stability of the system thus being increased.

[0011] In a preferred embodiment, the sealing material comprises atleast a second ply, which constitutes a barrier ply and is givensuitable properties so as to block the penetration of the cell by dirtand moisture from the environment. This type of sealing material isespecially suitable because the risk of impairment of the long-termstability of the system is reduced.

DESCRIPTION OF FIGURES

[0012] The invention will be described below with reference toaccompanying drawing figures, in which

[0013]FIG. 1 shows in cross section a sealed monolithic electrochemicalsystem comprising a number of cells,

[0014]FIG. 2 shows another embodiment of a monolithic electrochemicalsystem, in which series connection between a number of cells is effectedby alternate interconnection of end walls,

[0015]FIG. 3 shows a set of cells applied to a substrate,

[0016]FIG. 4 shows a flow diagram of the sealing process of themonolithic electrochemical system,

[0017]FIG. 4A shows a flow diagram of a set of part processes in thesealing process shown in FIG. 4,

[0018]FIG. 5 shows the pressing together of an electrochemical system bymeans of a flexible diaphragm,

[0019]FIG. 6 shows a soft pressing head,

[0020]FIG. 7 shows a two-chamber system for pressing an electrochemicalsystem together,

[0021]FIG. 8 shows an electrochemical system with a two-part sealingmaterial, and

[0022]FIG. 9 shows an electrochemical system with the outer areaspressed together hard.

MODES FOR CARRYING OUT THE INVENTION

[0023] In FIG. 1, a sealed monolithic electrochemical system 1comprising a number of cells 2A, 2B, 2C is shown in cross section. Eachcell 2A, 2B, 2C constitutes a porous structure and comprises a workingelectrode or photoelectrode 6, an insulating layer 7 and acounterelectrode 8. The cells 2A, 2B, 2C or the porous structures areapplied to a substrate in a pattern. The pattern is surrounded by anedge which consists of an inner edge which separates the individualcells from one another and an outer edge which surrounds a group ofcells which constitute said pattern. An example of such a system isdescribed in WO 97/16838, the description of which is incorporated inits entirety in this description.

[0024] The monolithic electrochemical system 1 comprises workingelectrodes in the form of nanoporous photoelectrodes 6 constructed on asubstrate. The substrate comprises a supporting layer 3 of completely orpartly transparent material and also a thin conductive layer 4 which isapplied to the supporting layer 3. The supporting layer 3 can be made ofglass or plastic, in which case the photoelectric system can be designedsomewhat flexibly. Each photoelectrode 6 is positioned on the thinconductive layer. The conductive layer is divided into a pattern of thindividing lines 5 where the conductive layer is removed, a set ofmutually insulated cells then being formed. The pattern preferablyconsists of a set of elongate rectangles, but can of course be designedin an arbitrary manner, although preferably in a surface-coveringpattern. An example of a suitable pattern is shown in FIG. 2, whichshows an electrochemical system 2 seen from above.

[0025] According to the embodiment shown in FIG. 2, the pattern of theporous structure as a set of rectangular cells 2A-2D. The cells arepositioned long side to long side. In this case, the outer edge isformed by a rectangle 40 which surrounds the set of cells and an inneredge is formed by a set of parallel lines 41 which separate the cellsfrom one another. A group of cells is series-connected in a knownmanner, for example as indicated below. Other surface-covering patternsare also conceivable, for example a set of hexagons. However, thepreferred embodiment with rectangles allows simple series-connectionbetween cells. In order to bring about series-connection between cellsin a simple manner, the plies of the cell are arranged in the embodimentshown in FIG. 1, where cells are interconnected side to side as follows:the photoelectrode 6 extends up to one edge of the conductive layer 4 ofthe cells while another edge is left free. The dividing lines 5 aredesigned with such a width that there is no risk of the photoelectrodecoming into contact with an adjacent cell.

[0026] The photoelectrode 6 is covered by a porous ply of an insulator7, which extends over one edge of the conductive layer and insulates thephotoelectrode 6 from a porous counterelectrode 8 which is located onthe insulator 7. The insulator 7 can preferably also constitute adiffuse reflector which reflects light which has passed through thephotoelectrode 6 without being absorbed in it, the degree of absorptionof the system being increased.

[0027] In a preferred embodiment, the counterelectrode 8 is applied insuch a manner that it essentially covers the insulator 7 and extends upto that layer on an adjacent cell not covered by insulator 7. In thismanner, series-connected cells are created, contacting 11, 12 having tobe provided only for the first and the last in an interconnected groupof cells.

[0028] The counterelectrodes 8 in the respective cells are separated byan interspace 9. It is important that the cells are insulated from oneanother so that electrolyte cannot leak out from the electrodes or theinsulator and bring about contact between electrodes in different cells.In order to ensure that this does not occur, the interspace can befilled with an insulating material. In a preferred embodiment, thisinsulating material consists of parts of the sealing material 10 whichis pressed into the interspace 9.

[0029] Before the electrochemical system 1 is sealed, an activesubstance is adsorbed, for example a light-absorbing colorant or anelectrochromic material for the photoelectrode 6. Furthermore,electrolyte is supplied to the porous structure consisting ofphotoelectrode 6, insulator 7 and counterelectrode 8. In a preferredembodiment, the electrolyte is supplied by means of a printing process,suitably screen printing. By using this method, the correct quantity ofelectrolyte can be supplied, so that the porous structure in each cellis filled but does not become overfull. If too much electrolyte issupplied, there is a risk that electrolyte will run out in theinterspace 9 between the cells, giving rise to a risk ofshort-circuiting between the cells. In another embodiment, theelectrolyte is supplied by the porous structure being allowed to adsorbelectrolyte during a dispensing process.

[0030] In another embodiment, which is shown in FIG. 3,series-connection between a number of cells 2A, 2B and 2C is effected byend walls of the cells being connected as described below. In thisembodiment, the cells are in a pattern in which each cell is rectangularand has two long sides and two end walls. The cells are formed on asubstrate with a ply 4 of conductive material. The cells are insulatedfrom one another by tracks 5 of the conductive material being etchedaway. Each cell comprises an anode 6 made of porous material, and in thepresent case this anode consists of a light-sensitive photoelectrode. Aninsulator 7 made of porous material is applied to the anode 6. Acounterelectrode 8 made of porous material is applied to said insulator7. In order to bring about series-connection between the cells, thecells are connected in such a manner that the anode of one cell isconnected to the counterelectrode of the next cell. In the embodimentshown in FIG. 2, this is effected by the etched-away tracks 5 beingdesigned in a zig-zag pattern, which produces an L-shaped pattern ofconductive surfaces consisting of a set of Ls, having a back 13 and afoot 14, facing one another so that the protuberance from one L tends tobe located directly adjacent to the next L. The photoelectrode 6 islocated entirely within the back, that is to say the elongate part, ofan L-shaped area. The insulator 7 is positioned so that it covers thephotoelectrode and extends in slightly onto the foot 14 of the L-shapedarea of an adjacent cell, that is to say the insulator 7 bridges theetched-away track 5 within an area corresponding to the width of thecell. Series-connection is effected by the counterelectrode 8 of onecell being allowed to extend into the conductive layer 4 of an adjacentcell. In the embodiment shown in FIG. 3, this is brought about by virtueof the counterelectrode 8 extending into the foot 14 of an L-shaped areaof an adjacent cell. FIG. 3 also shows an encapsulating material 10A anda cover layer 10B which together constitute a sealing material 10. In apreferred embodiment, the encapsulating material 10A consists of anadhesion ply 19A, and the cover layer 10B consists of an adhesion layer19B and a barrier layer 19C.

[0031] After the electrolyte has been supplied to the porous structure,the electrochemical system 1 is sealed by means of a sealing material 10according to the invention using a method described below in connectionwith FIG. 4.

[0032] In a first method step 20, a sealing material 12 is applied tothe substrate 3 in such a manner that it completely covers the cells2A-2C and their porous structure to form a sealed monolithicphotoelectric system comprising a front plane consisting of saidsubstrate and the porous structure, and a rear plane consisting of thesealing material. The sealing material comprises at least one ply ofplastic, preferably a thermoplastic such as, for example, methacrylicacid polyethylene, which is intended, on heating, to adhere to theunderlying substrate and, if appropriate, the porous structure locatedon the substrate. In a preferred embodiment, the sealing materialconsists of a laminate in which an adhesion ply of plastic and a barrierply with low or no air and liquid permeability, for example an aluminumfoil. In another preferred embodiment, the sealing material comprises onthe one hand an adhesion ply of plastic which is intended, as above, tobear against the substrate, and on the other hand a laminate consistingof a plastic layer and an aluminum layer where the plastic layer isintended to adhere to said adhesion ply. The plastic layer is bonded tothe aluminum layer in a manner well-known to the person skilled in theart, for example by gluing. By using an intermediate ply, a good jointis brought about because the more flexible adhesion ply takes on theshape of the support more effectively then the less flexible aluminumply.

[0033] In order to ensure that adequate tightness against liquidpenetration through the edge of the adhesion ply is obtained, theadhesion ply is, in a preferred embodiment, designed with a thickness ofless than 50 μm and, in a further preferred embodiment, with a thicknessof less than 30 μm. With said thicknesses, a ply is obtained, which issufficiently thin that edge throughflow does not impact negatively onthe long-term stability of the enclosed cells at the same time as thethickness is sufficiently great to be easy to handle.

[0034] In a second method step 21, the sealing material is pressedtogether with the substrate and the cells located on the substrate. Thesealing is effected by a front plane consisting of said substrate andthe porous structure and a rear plane consisting of the sealing materialbeing pressed together while subjected to heat, the adhesion ply meltingtogether with the front plane, and sealing along the edge of the patternbeing permitted. This sealing insulates the individual cells from oneanother along the inner edge of the pattern and thus prevents leakage ofelectrolyte between the cells and also insulates the group of cellswhich a pattern constitutes from the surrounding environment at theouter edge of the pattern and thus prevents dirt or moisture penetratingthe cells. Alternative preferred embodiments of the pressing togetherare indicated below.

[0035] Furthermore, certain preferred part processes during sealing 21are shown symbolically in FIG. 4A. In a first part process 22, anadhesion ply of plastic is first positioned against the front plane, andthereon a laminate consisting of an adhesion ply, preferably made ofplastic, and a barrier layer, preferably made of aluminum. In the eventthat use is made of a plastic layer and an aluminum layer, the plasticlayer is bonded to the aluminum layer in a manner well-known to theperson skilled in the art, for example by gluing. By using anintermediate ply, a good joint is brought about because the moreflexible adhesion ply adapts to the shape of the support moreeffectively than the less flexible aluminum ply. FIG. 8 shows the frontplane 19, the adhesion ply 19A and the barrier ply of adhesion layer 19Band barrier layer 19C. The adhesion layer 19B has the function ofjoining the barrier layer 19C and the adhesion ply 19A together. Theadhesion ply preferably consists of a thermoplastic.

[0036] In a second part process 23, the front plane and the sealingmaterial are subjected to an underpressure, making it possible to reducethe presence of dirt and moisture in the cells.

[0037] In a third part process 24, the front plane and the sealingmaterial are pressed together by a flexible pressing tool, good sealingaround both inner and outer edges.

[0038] In order to obtain still better sealing around the outer edge,the outer edge can moreover, a little way outside the cells, for example2-5 mm from the edge of the cells, be pressed together by a hardpressing tool in a fourth part process 25. This pressing together makesany adhesion ply 19A present thinner, the risk of penetration of dirtand moisture from the environment penetrating after joining togetherbeing reduced. FIG. 9 shows a group of cells which are pressed togetherby a hard pressing tool within two areas 26A and 26B essentiallysurrounding a grouping of cells 2A-2D. In an area 26C, 26D around eachof the contacts 11, 12, the cell grouping is not pressed together inorder to avoid the aluminum layer in the barrier ply being pressedtogether with the conductive ply on the substrate. In order to ensurethat any flashover between the conductive ply and the aluminum layer inthe areas 26A and 26B does not impact negatively on the cell grouping,these areas are separated by etched-away tracks 26E and 26F, the areaswhere hard pressing takes place being electrically insulated from thecell grouping as a whole.

[0039] The part processes indicated above can be combined individuallyto obtain separate preferred embodiments of the invention.

[0040] In a preferred embodiment, the pressing together is carried outby a flexible pressing tool. A flexible pressing tool means that thepressing tool is allowed to be deformed sufficiently to allow thepressing tool to be deformed for access into the interspaces between thecells, the sealing material being pressed in against the front plane sothat the sealing material is pressed against the cells and down into theinterspaces between the cells and also around the edges of the pattern.FIGS. 5, 6 and 7 show examples of embodiments of flexible pressingtools.

[0041]FIG. 5 shows the pressing together of a monolithic photoelectricsystem by means of a flexible diaphragm 15A. The electrochemical system1 is placed on a support 15B, after which it is covered by the flexiblediaphragm 15A. The flexible diaphragm can suitably be made of rubber.The electrochemical system is then subjected to pressure via thediaphragm 15A, and heat is supplied, sealing being effected. In apreferred embodiment, the pressure on the diaphragm 15A is brought aboutby the space 16 around the electrochemical system 1 being subjected toan underpressure. This underpressure reduces the presence of moistureand impurities in the cells before sealing takes place, the quality ofthe cells being improved. The support 15B can also be designed as aflexible diaphragm.

[0042] In a preferred embodiment, the pressing together takes placeunder pressure which is obtained from flexible diaphragms which surroundthe monolithic electrochemical system. By making use of a flexiblediaphragm, a uniform pressure is obtained over the entire monolithicelectrochemical system and good sealing is obtained in theabovementioned interspaces 9 between the cells.

[0043] In a preferred embodiment, the pressure is obtained by virtue ofthe monolithic electrochemical system being placed in a pocket betweentwo flexible diaphragms and said pocket being subjected to anunderpressure, the pressure of the environment pressing the monolithicelectrochemical system together. This underpressure also contributes toreducing moisture and the presence of dirt in the porous structurebefore sealing finally takes place.

[0044]FIG. 6 shows an alternative embodiment where the pressing togetheris effected by a pressing head 17 comprising a pressing surface 18 madeof soft material, for example rubber, pressing together of the sealingmaterial and the front plane being permitted so that the sealingmaterial is pressed against the cells and down into the interspacesbetween the cells and also around the edges of the pattern. According toa preferred embodiment, this type of pressing can take place in achamber subjected to an underpressure, making it possible to reduce thepresence of dirt and moisture in the finished product.

[0045] In an illustrative embodiment, the monolithic electrochemicalsystem is placed in a heating furnace which heats the monolithicelectrochemical system to roughly 100° C., heating from room temperaturetaking place over roughly 30 minutes. The material is then cooledslowly.

[0046] According to an alternative method, the electrochemical system issealed by the front plane and the sealing material being placed in achamber which is subjected to an underpressure. According to a preferredembodiment, in order to permit the evacuation to reduce further thepresence of dirt and moisture, the front plane and the sealing materialare separated by a gap for a period of time while subjected to theunderpressure.

[0047] When the front plane and the sealing material have reached thecorrect temperature, the front plane is pressed together with thesealing material.

[0048] In an embodiment of the invention, the pressing together iscarried out by using a two-part chamber as shown in FIG. 7. The chamber30 is formed in a housing 31 and comprises a first and a second partchamber 34, 35 separated by a flexible diaphragm 32. The electrochemicalsystem 33 to be joined together is placed in one of the part chambers.An air pump (not shown) is or can be connected to the comb so as to makeevacuation of both the first and the second part chamber possible. Tothis end, the housing 31 can be provided with a communication ductbetween the first and the second chamber, the communication ductcomprising a check valve positioned so that evacuation of the first andsecond chamber can be effected jointly, but air does not flow from thesecond to the first chamber when air is subsequently introduced in orderto allow pressing together of the front plane and the sealing materialof the electrochemical system.

[0049] The invention is not limited to the embodiments described abovebut can be varied within the scope of the patent claims below. Forexample, the electrochemical system can consist of aphotoelectrochemical system, that is to say a solar cell, or a displayin which elements constitute, for example, letter segments. In anembodiment, it is conceivable to encapsulate a display alongside a solarcell. In this case, different electrolytes will be used for the displayand the solar cell, which are encapsulated simultaneously. Furthermore,both rear plane and front plane can comprise additional plies; forexample, a colored layer can be located between the adhesion ply 19A andthe adhesion layer 19B in order to give the product a desiredappearance, or alternatively these or other layers forming part of theproduct can be colored.

1. A method for manufacturing a sealed monolithic electrochemicalsystem, which method comprises the following method steps: applicationof electrolyte to a pattern of a porous structure located on asubstrate, which structure constitutes at least one monolithicelectrochemical cell and comprises a working electrode, an insulatinglayer and a counterelectrode application of a sealing materialsurrounding said porous structure to form at least one sealed monolithicelectrochemical system comprising a front plane consisting of saidsubstrate and the porous structure and a rear plane consisting of thesealing material characterized in that the following method steps areperformed after said application of electrolyte: said front plane andrear plane are heated and pressed together, sealing along the edge ofthe pattern of the porous structure being permitted by virtue of aplastic layer forming part of the sealing material being melted andjoined together with said front plane.
 2. The method as claimed in claim1, characterized in that the front plane and the rear plane are pressedtogether by a flexible pressing tool.
 3. The method as claimed in claim1 or 2, characterized in that, in conjunction with said heating andpressing together, said front plane and rear plane are subjected to anunderpressure, evacuation of moisture and gases from the porousstructure being permitted.
 4. The method as claimed in any one of claims1-3, characterized in that said front plane and rear plane are pressedtogether by means of a flexible diaphragm.
 5. The method as claimed inany one of the preceding claims, characterized in that said front planeand rear plane are placed between flexible diaphragms which togetherform a pocket surrounding the front plane and the rear plane, and inthat said pocket is subjected to an underpressure, said pressingtogether of the front plane and the rear plane then taking place.
 6. Themethod as claimed in any one of the preceding claims, characterized inthat the front plane and the rear plane are placed in a first chamber,where the front plane and the rear plane are subjected to anunderpressure, and in that the front plane and the rear plane arepressed together.
 7. The method as claimed in claim 6, characterized inthat said front plane and rear plane are separated from one another by agap, while subjected to an underpressure, for a period of time beforepressing together.
 8. The method according to claim 6 or 7,characterized in that the front plane and the rear plane are placed in atwo-chamber system, in which a first and a second chamber are separatedby a flexible diaphragm, in that at least the chamber in which the frontplane and the rear plane are placed is subjected to an underpressure,and in that the front plane and the rear plane are pressed together byvirtue of a positive pressure in the second chamber pressing thediaphragm against the front plane or the rear plane.
 9. The method asclaimed in any one of the preceding claims, characterized in that saidelectrolyte is applied to said pattern of the porous structure by meansof a printing process.
 10. The method as claimed in any one of thepreceding claims, characterized in that said electrolyte is applied tosaid pattern of the porous structure by means of a dispensing process.11. The method as claimed in any one of the preceding claims,characterized in that the rear plane consists of a plastic film, and inthat said rear plane and front plane are joined together by melting theplastic film and the front plane together.
 12. The method as claimed inany one of the preceding claims, characterized in that the substratecomprises a supporting layer made of a plastic or glass material. 13.The method as claimed in any one of the preceding claims, characterizedin that the rear plane comprises an adhesion ply of plastic, and also alaminate comprising at least an adhesion layer and a barrier layer, inthat the adhesion ply is applied to the front plane and said laminateforming part of the rear plane is placed over said adhesion ply, and inthat said front plane and rear plane are joined together to form asealed monolithic electrochemical system by melting together theadhesion ply, the front plane and the adhesion layer.
 14. The method asclaimed in any one of the preceding claims, characterized in that saidfront plane and rear plane are pressed together by a hard pressing headwithin an area which surrounds a grouping of electrochemical cells. 15.The method as claimed in claim 14, characterized in that said area has aminimum distance to an outer edge surrounding said grouping of cellsexceeding 1 mm.
 16. A sealed monolithic electrochemical systemcomprising a substrate supporting a pattern, located on said substrate,of a porous structure which comprises a working electrode, an insulatinglayer and a counterelectrode, electrolyte absorbed in said substrate forforming at least one electrochemical cell and contacts for saidelectrodes for interconnection with at least one electric circuit and asealing material located on said substrate and covering said porousstructure, characterized in that the sealing material comprises anadhesion ply 19A of plastic which is applied to said substrate andporous structure 19 and a laminate 19B, 19C comprising at least anadhesion layer 19B and a barrier layer 19C, in which the adhesion layer19B is placed over said adhesion ply 19A, and in that said substrate,porous structure and sealing material are joined together to form asealed monolithic electrochemical system by melting the substrate, theadhesion ply 19A and the adhesion layer 19B together.
 17. The sealedmonolithic electrochemical system as claimed in patent claim 16,characterized in that said barrier layer 19C consists of a metal foil.18. A method for producing a tight connection between a front planeconsisting of an at least partly transparent substrate with a pattern ofa porous structure constituting at least one monolithic electrochemicalelectrode and a rear plane comprising at least one ply of plastic whichis intended to bear against the front plane, characterized in that saidplane is subjected to an underpressure allowing evacuation of moistureand gases from the porous structure, said planes are heated and pressedtogether, sealing along the edge of the pattern of the porous structurebeing permitted.